1. Field of the Invention
The invention relates to an illumination device; in particular, to an illumination device with adjustable luminance and a luminance adjustment method thereof.
2. Description of the Prior Art
Except a lamp with fixed luminance providing single luminance, the current illumination device can include luminance adjusting mechanisms, such as a tri-electrode AC switch (TRIAC), a pulse width modulation (PWM) circuit, or a multi-stage switch, to adjust the luminance of the lights outputted by the illumination device according to illumination requirements.
FIG. 1A illustrates a schematic diagram of the circuit of a conventional illumination device 10; FIG. 1B illustrates a schematic diagram of the relationship between the light luminance of a light source module 40 and the outputted current of a tri-electrode AC switch 30 shown in FIG. 1A. As shown in FIG. 1A, the conventional illumination device 10 includes an external power supply 20, the tri-electrode AC switch 30, and the light source module 40. And, the user can adjust the tri-electrode AC switch 30 to adjust the current outputted to the light source module 40 and the luminance of the lights generated by the light source module 40. As shown in FIG. 1B, there are positive correlation and linear relationship between the luminance of the lights generated by the light source module 40 and the outputted current of the tri-electrode AC switch 30.
The conventional illumination device 10 can achieve linear control of the luminance through the tri-electrode AC switch 30. However, because the outputted current of the tri-electrode AC switch 30 is not stable enough, the LED with higher current sensitivity may have luminance flicker problems due to the unstable outputted current amplitude of the tri-electrode AC switch 30. In addition, there is also the problem of poor energy converting efficiency during the process of the tri-electrode AC switch 30 converting the external power into the current. Therefore, the tri-electrode AC switch 30 is not suitable to be used in the LED light source module 40.
FIG. 2A illustrates a schematic diagram of the circuit of another conventional illumination device 12; FIG. 2B illustrates a schematic diagram of the relationship between the light luminance of the light source module 40 and the switching points of a switch 60 shown in FIG. 2A. As shown in FIG. 2A, the conventional illumination device 12 includes the light source module 40, a control module 50, and the switch 60. The switch 60 conducts the voltage of the external power supply 20 to the control module 50 only when it is switched from the open circuit state (OFF) to the conduction state (ON). After every time the control module 50 receives the external power voltage, the control module 50 will increase the current outputted to the light source module 40 according to a setup value. In this way, the user has to switch the switch 60 several times between the open circuit state and the conduction state to adjust the outputted voltage of the control module 50 and the light luminance generated by the light source module 40.
When the user uses the above-mentioned conventional illumination device 12, it is inconvenient for the user that he/she has to switch on and off the switch 60 according to different light luminance. In addition, the control module 50 shown in FIG. 2A can only increase the amplitude of the outputted current in a step type. Therefore, the user cannot control the conventional illumination device 12 to obtain the light luminance between two steps. In other words, the conventional illumination device 12 shown in FIG. 2A cannot achieve the linear control of illumination.
Therefore, how to achieve linear illumination output and avoid luminance flicker at the same time and how to increase electrical energy converting efficiency will be important issue for illumination adjustment of the current illumination device.